Polyarylene sulfide is a high performance polymer that can withstand high thermal, chemical, and mechanical stresses. Due to its relatively slow crystallization rate, however, injection molding of parts from polyarylene sulfide can be challenging. For example, to achieve the desired degree of crystallization, molding is generally conducted at a high mold temperature (˜130° C. or more) and for a relatively long cycle time. Unfortunately, high mold temperatures typically dictate the need for expensive and corrosive heating mediums (e.g., oil).
Attempts to address the problems noted above have generally involved the inclusion of nucleating agents in the polymer composition to help improve the crystallization properties. For instance, boron nitride has often been utilized as a nucleating agent. Boron nitride nucleating agents exhibiting particular characteristics have been developed in an attempt to further improve characteristics of the polymers. For instance hexagonal boron nitride having a particular aspect ratio (e.g., greater than 2) and/or delaminated boron nitride particles with very high aspect ratios and very small dimensions have been formed. High purity boron nitride particles that exhibit high crystallinity have also been utilized as nucleating agents. In general, it has been assumed that the best route to enhancing the desirable characteristics of the boron nitride is by decreasing the size and increasing the purity of the particles.
To date, however, such attempts have not been fully satisfactory. In fact, the problems have become even more pronounced as various industries (e.g., electronic, automotive, etc.) are now demanding injection molded parts with very small dimensional tolerances. In these applications, the polymer must have good flow properties so that it can quickly and uniformly fill the small spaces of the mold cavity. It has been found, however, that conventional polyphenylene sulfides that manage to meet the requisite high flow requirement utilize nucleating agents that tend to require a long cooling cycle, which can be a very costly and time consuming step.
As such, a need exists for suitable nucleating agents for polyarylene sulfide that can provide a relatively short cycle time while still achieving good mechanical properties.